clam

1. a ↑shellfish you can eat that has a shell in two parts that open up:
clam chowder (=a type of soup)
2. as happy as a clam American English informal very happy
3. American English informal someone who does not say what they are thinking or feeling
II. clam² BrE AmE verb (past tense and past participle clammed, present participle clamming)
clam up phrasal verb
informal to suddenly stop talking, especially when you are nervous or shy:
A sensitive child is likely just to clam up.

Oxford Advanced Learner's Dictionary

clam

clam [clam clams clammed clamming] [klæm] [klæm]

noun

a shellfish that can be eaten. It has a shell in two parts that can open and close
• clam chowder/soup
• The moment I mentioned the children he closed up like a clam (= became silent and refused to discuss the topic).
Word Origin:
early 16th cent.: apparently from earlier clam ‘a clamp’, from Old English clam, clamm ‘a bond or bondage’, of Germanic origin; related to Dutch klemme, German Klemme, also to clamp.

Derived: clam up

Cambridge Advanced Learner's Dictionary

clam / klæm / noun [ C ]

a type of sea creature with a shell in two parts that can close together tightly, and a soft body that can be eaten

Collins Advanced Learner’s English Dictionary

clam

[klæ_m]
clams, clamming, clammed
N-COUNT
Clams are a kind of shellfish which can be eaten.
Phrasal Verbs:
- clam up

Merriam-Webster's Advanced Learner's Dictionary

¹clam /ˈklæm/ noun, pl clams
1 [count] : a type of shellfish that lives in sand or mud, has a light-colored shell with two parts, and is eaten both cooked and raw
• steamed clams
• clam chowder
- see color picture
2 clams [plural] US slang somewhat old-fashioned : dollars
• He won 20 clams [=(more commonly) bucks] playing poker.
(as) happy as a clam US informal : very happy
• She spent the afternoon reading and was as happy as a clam.